Rubber O-rings that are able to produce high seal ability are used to inhibit leakage of a high-pressure gas, the pressure of which varies less, i.e., is held substantially constant. As the O-rings, O-rings according to “B 2401” of Japanese industrial Standard (JIS) may be used.
Resin seal members are used to inhibit leakage of a gas, the pressure of which varies frequently in a great range between a high pressure and a low pressure.
Although the O-rings advantageously produce high seal ability for the gas with less pressure variation, they may generate a blistering phenomenon if they are used to inhibit leakage of the gas with the above mentioned pressure variation, and are therefore unable to be used to inhibit leakage of the gas with the pressure variation. The blistering phenomenon is such that, when a rubber member is exposed to a high-pressure gas, the high-pressure gas permeates the rubber member and is held therein, and the held high-pressure gas rapidly expands and is about to exit to outside when the pressure of the surrounding gas decreases rapidly, leading to minute bubbles in the interior of the rubber member. Likewise, the blistering phenomenon occurs in the O-rigs. Upon occurrence of the blistering phenomenon, the O-rings lose their seal ability.
In the case of the gases with small molecular weight and high permeability, such as the hydrogen gas and the helium gas, the O-rings tend to increase the amount of permeating gas as the gas pressure increases. Therefore, the O-rings are unable to achieve high seal ability for the highly permeable gases when they are used alone.
The resin seal members are used to inhibit leakage of the gas with pressure variation because it does not generate the blistering phenomenon and has low gas permeability. However, the resin seal members are less flexible than the rubber O-rings and are unable to achieve seal ability as high as that of the rubber O-rings. In addition, the resin seal members are unable to be deformed in response to the rapid pressure variation, and are thus unable to achieve a high seal ability. Especially when the gas pressure turns from a high pressure to a low pressure, the gas tends to leak.
A seal structure that is suitably used to inhibit leakage of the gas, the pressure of which tends to vary greatly and to become a high pressure, has not been created yet.